Load operation control system

ABSTRACT

A drive shaft rotates a load. A drive support rotates the drive shaft and supports a radial load of the drive shaft in a non-contact manner, by an electromagnetic force generated by the flow of a current within a predetermined current range through the drive support. A control section controls an operation of the load based on a magnetic flux margin degree expressed by the difference between a total magnetic flux amount generated at the drive support and a predetermined limit of the total magnetic flux amount for the drive support. The total magnetic flux amount includes driving magnetic flux and the supporting magnetic flux in a predetermined operation region of the load. The driving magnetic flux is generated at the drive support for rotating the drive shaft. The supporting magnetic flux is generated at the drive support for supporting a radial load of the drive shaft.

TECHNICAL FIELD

The present invention relates to a system for controlling an operatingcondition of a load connected to a drive shaft, which is rotated andsupported in a non-contact manner by a drive support.

BACKGROUND ART

There is a type of compressors that is called a turbo compressor. Turbocompressors are used in a variety of applications such as airconditioners.

As disclosed in Patent Document 1, turbo compressors have a problemcalled surging. Surging is a phenomenon in which, for example, when aload of a compressor in operation is suddenly changed from a high loadto no load, the flow rate of the fluid (refrigerant) in the entire flowpath including the compressor becomes unstable, and pipes or otherelements which constitute the compressor and the flow path resonate, sothat the pressure and the flow rate periodically fluctuate. Surgingcauses not only the instable operating state of the compressor, but alsodamage to the compressor.

CITATION LIST Patent Documents

Patent Document 1: Japanese Unexamined Patent Publication No.2013-127221

SUMMARY OF THE INVENTION Technical Problem

Surging occurs when the operating state of the compressor enters thesurging region. Thus, in the above-mentioned Patent Document 1, theoperating state of the compressor is controlled so as not to enter thesurging region by reducing a sudden decrease in the flow rate before andafter the transition of the load state of the compressor.

That is, the compressor of Patent Document 1 is operated only in thesteady state operation region. This configuration of the compressor ofPatent Document 1 results in that the use of the compressor is limitedand that the range of situations in which the compressor is operable isnarrow.

The problem of limited use occurs not only in the compressors, but mayalso occur, for example, in a load such as pumps that may experiencesurging.

In view of the foregoing background, it is an object of the presentinvention to increase the width of operation of a load, such as acompressor, which may experience surging.

Solution to the Problem

A first aspect of the present disclosure is directed to a load operationcontrol system including: a drive shaft (20) which rotates a load; adrive support (50) which rotates the drive shaft (20) and supports aradial load of the drive shaft (20) in a non-contact manner, by anelectromagnetic force generated by flow of a current within apredetermined current range through the drive support (50); and acontrol section (91 a) which controls an operating condition of the loadbased on a magnetic flux margin degree expressed by a differencebetween: a total magnetic flux amount including driving magnetic fluxand supporting magnetic flux; and a predetermined limit of the totalmagnetic flux amount for the drive support (50), the driving magneticflux being generated in the drive support (50) for rotating the driveshaft (20) and the supporting magnetic flux being generated at the drivesupport (50) for supporting the radial load of the drive shaft (20) in apredetermined operation region of the load.

In this aspect, it is possible to extend the operation region of theload as much as possible by changing the operating condition of the loadin accordance with the magnetic flux margin degree of the drive support(50). Specifically, the radial load may increase if the operation regionof the load is extended from a steady state operation region to a regionwhere the rotating stall occurs. However, the control section (91 a)changes the operating condition of the load in accordance with themagnetic flux margin degree of the drive support (50), which allows theextension of the operation region to the maximum controllable extent.

A second aspect of the present disclosure is an embodiment of the firstaspect. In the second aspect, the drive support (50) has at least onebearingless motor (60, 70) having a set of a rotor (61, 71) and a stator(64, 74) to rotate the drive shaft (20) and supporting the radial loadof the drive shaft (20) in a non-contact manner.

In the bearingless motor (60, 70), it is possible to change the ratiobetween the supporting magnetic flux and the driving magnetic flux inaccordance, for example, with the operating state of the load and themagnetic flux margin degree. That is, the control (such as decreasingthe driving magnetic flux and increasing the supporting magnetic flux,which are generated in the bearingless motor (60, 70)) can be performed,while ensuring a certain magnetic flux margin degree, so that the loadcan withstand the surging phenomenon in the case in which the operationregion of the load is extended. The load is therefore operable in awider variety of operating state without a problem.

A third aspect of the present disclosure is an embodiment of the secondaspect. In the third aspect, the control section (91 a) calculates, asthe total magnetic flux amount, an amount of magnetic flux at a slotwhere a total value of the driving magnetic flux and the supportingmagnetic flux is the largest among a plurality of slots formed in thestator (64, 74).

A fourth aspect of the present disclosure is an embodiment of the thirdaspect. In the fourth aspect, the control section (91 a) calculates thetotal magnetic flux amount, using a sum of the driving magnetic flux,the supporting magnetic flux, and further magnetic flux of a permanentmagnet (63, 73) included in the rotor (61, 71) as the total value.

It is therefore possible to obtain an accurate total magnetic fluxamount generated in the bearingless motor (60, 70).

A fifth aspect of the present disclosure is an embodiment of any one ofthe first to fourth aspects. In the fifth aspect, the load is a turbocompressor (1) which compresses a refrigerant in a refrigerant circuit(110) configured to perform a refrigeration cycle, and the controlsection (91 a) if the magnetic flux margin degree exceeds apredetermined value, adjusts at least one of a rotational speed of theturbo compressor (1) and a flow rate of the refrigerant such that atemperature of the refrigerant discharged from the turbo compressor (1)increases, and if the magnetic flux margin degree is below thepredetermined value, adjusts at least one of the rotational speed of theturbo compressor (1) and the flow rate of the refrigerant such that thetemperature of the refrigerant discharged from the turbo compressor (1)decreases.

If the magnetic flux margin degree exceeds the predetermined value, itis possible to determine that the drive support (50) has a margin interms of magnetic flux. In this case, an increase in the temperature ofthe refrigerant discharged from the turbo compressor (1) allows anincrease in the head (compression work) of the turbo compressor (1).That the turbo compressor (1) becomes operable in a region where thehead is high means that the refrigerant circuit (110) is capable ofperforming the refrigeration cycle even in, for example, ahigh-temperature outdoor environment, which means that the operationregion of the load is extended.

On the other hand, if the magnetic flux margin degree is below thepredetermined value, it is possible to determine that the drive support(50) does not have a margin in terms of magnetic flux. In such a case,the temperature of the refrigerant discharged from the turbo compressor(1) is decreased, thereby decreasing the head (compression work) of theturbo compressor (1). It is therefore possible to avoid the occurrenceof surging and rotating stall in the turbo compressor (1).

A sixth aspect of the present disclosure is an embodiment of the fifthaspect. In the sixth aspect, the load operation control system furtherincludes an update section (91 b) which updates the predeterminedoperation region, based on an operating state of the turbo compressor(1) at a time when the control section (91 a) increases the temperatureof the refrigerant discharged from the turbo compressor (1).

This configuration allows the next operation of the turbo compressor (1)to be performed with reference to the extended operation region.

A seventh aspect of the present disclosure is an embodiment of any oneof the first to fourth aspects. In the seventh aspect, the load is aturbo compressor (1) which compresses a refrigerant in a refrigerantcircuit (110) configured to perform a refrigeration cycle, and thecontrol section (91 a) if the magnetic flux margin degree exceeds apredetermined value, adjusts at least one of a rotational speed of theturbo compressor (1) and a flow rate of the refrigerant such that anoutput of an air conditioner (100) having the refrigerant circuit (110)decreases, and if the magnetic flux margin degree is below thepredetermined value, adjusts at least one of the rotational speed of theturbo compressor (1) and the flow rate of the refrigerant such that theoutput of the air conditioner (100) increases.

The lower the output of the air conditioner (100) is, the more likely itis that the turbo compressor (1) enters the surging region. In contrast,the higher the output of the air conditioner (100) is, the less likelyit is that the turbo compressor (1) enters the surging region.

If the magnetic flux margin degree exceeds the predetermined value andthe drive support (50) has a margin in terms of magnetic flux, it ispossible to use the margin of the magnetic flux to generate thesupporting magnetic flux. Thus, the output of the air conditioner (100)is intentionally reduced to cause the operating state of the turbocompressor (1) to transition to the region where rotating stall andsurging occur. This means that the operation region of the load isextended.

If the magnetic flux margin degree is below the predetermined value andthe drive support (50) does not have a margin in terms of magnetic flux,it means that the drive support (50) does not have enough magnetic fluxthat can be used for the generation of the supporting magnetic flux.Thus, the output of the air conditioner (100) is increased to cause theturbo compressor (1) to operate in a region from which it is less likelythat the turbo compressor (1) enters the region where rotating stall andsurging occur. It is therefore possible to avoid the occurrence ofsurging and rotating stall in the turbo compressor (1).

An eighth aspect of the present disclosure is an embodiment of theseventh aspect. In the eighth aspect, the load operation control systemfurther includes an update section (91 b) which updates thepredetermined operation region, based on an operating state of the turbocompressor (1) at a time when the control section (91 a) decreases theoutput of the air conditioner (100).

This configuration allows the next operation of the turbo compressor (1)to be performed with reference to the extended operation region.

Advantages of the Invention

According to the aspects of the present disclosure, the operation regionof a load is extended to a maximum operable extent, which allows theload driven by the drive support (50) to be operated in a wider varietyof operating state.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a piping system diagram of an air conditioner.

FIG. 2 is a diagram illustrating an example configuration of acompressor.

FIG. 3 is a diagram illustrating a transverse section of an exampleconfiguration of a first bearingless motor.

FIG. 4 is the transverse section of the first bearingless motor, showingmagnetic flux of magnet and driving magnetic flux.

FIG. 5 is the transverse section of the first bearingless motor, showingthe magnetic flux of the magnet and supporting magnetic flux.

FIG. 6 is the transverse section of the first bearingless motor, showingthe magnetic flux of magnet, the driving magnetic flux, and thesupporting magnetic flux.

FIG. 7 is a transverse section of a second bearingless motor, showingmagnetic flux of magnet, driving magnetic flux, and supporting magneticflux.

FIG. 8 is a graph for explaining an operation region of a turbocompressor.

FIG. 9 is a graph for explaining extension control for the operationregion.

FIG. 10 is a graph for explaining a mechanism of surging.

FIG. 11 is a flowchart indicating the flow of extension control for theoperation region according to a first embodiment.

FIG. 12 is a flowchart indicating the flow of extension control for theoperation region according to a second embodiment.

DESCRIPTION OF EMBODIMENTS

Embodiments of the present disclosure will now be described in detailwith reference to the drawings. The embodiments below are merelyexemplary ones in nature, and are not intended to limit the scope,applications, or use of the present invention.

<<First Embodiment>>

An example in which an air conditioner includes a compressor having amagnetic bearing device will be described below.

<General Configuration>

FIG. 1 is a piping system diagram of an air conditioner (100) accordingto a first embodiment of the present invention. As illustrated in FIG.1, the air conditioner (100) is intended for air-conditioning the air inthe room, and includes a refrigerant circuit (110) which is a closedcircuit filled with refrigerant. The refrigerant circuit (110) includesa turbo compressor (1), a condenser (120), an expansion valve (130), andan evaporator (140) which are connected to one another via refrigerantpipes. The turbo compressor (1) according to the first embodiment isdriven by bearingless motors (60, 70).

Although not shown, a sensor for detecting a refrigerant pressure and asensor for detecting a refrigerant temperature are also provided in therefrigerant circuit (110).

An example will be described in the first embodiment, in which thecondenser (120) and the evaporator (140) are used so that heat isexchanged between the refrigerant and an aqueous medium. That is, theair conditioner (100) according to the first embodiment is a so-calledchiller unit which cools the interior of the room by means of theaqueous medium.

Specifically, not only the refrigerant circuit (110) but also anoutdoor-side water circuit (150), in which the aqueous mediumcirculates, are connected to the condenser (120). In the condenser(120), the refrigerant dissipates heat to the aqueous medium(circulating water) in the outdoor-side water circuit (150) which hascirculated from the outdoor side. The refrigerant is therefore cooledand condensed. The aqueous medium flowing out of the condenser (120)dissipates heat outdoors.

Not only the refrigerant circuit (110) but also an indoor-side watercircuit (160), in which the aqueous medium circulates, are connected tothe evaporator (140). In the evaporator (140), the refrigerant absorbsheat from the aqueous medium (circulating water) in the indoor-sidewater circuit (160) which has circulated from the indoor side. Therefrigerant therefore evaporates. The aqueous medium flowing out of theevaporator (140) circulates through the indoor-side water circuitprovided in the room, thereby cooling the interior of the room.

<Configuration of Turbo Compressor>

FIG. 2 is a diagram illustrating an example configuration of the turbocompressor (1) according to the first embodiment. As illustrated in FIG.2, the turbo compressor (1) includes a casing (2), a compressionmechanism (3), a drive shaft (20), touchdown bearings (30, 31), a thrustmagnetic bearing (40), and a drive support (50).

Among these elements, the drive shaft (20), the touchdown bearings (30,31), the thrust magnetic bearing (40), and the drive support (50)constitute a load operation control device (10), which corresponds to aload operation control system, together with a controller (90) and otherelements which will be described later. The casing (2) and thecompression mechanism (3) will be described first.

In the following description, the “axial direction” refers to adirection of the axis of rotation, which is the direction of the axis ofthe drive shaft (20). The “radial direction” refers to a directionperpendicular to the axial direction of the drive shaft (20). The “outercircumferential side” refers to a side farther from the axis of thedrive shaft (20). The “inner circumferential side” refers to a sidecloser to the axis of the drive shaft (20).

—Casing—

The casing (2) is in a cylindrical shape with its both ends closed, andis arranged such that its axial direction extends horizontally. Thespace in the casing (2) is partitioned by a wall (2 a). The space on theright of the wall (2 a) constitutes an impeller chamber (S1) foraccommodating an impeller (3 a) of the compression mechanism (3). Thespace on the left of the wall (2 a) constitutes an electric motorchamber (S3) for accommodating first and second bearingless motors (60,70) included in the load operation control device (10). The drive shaft(20) extending in the axial direction of the casing (2) connects theimpeller (3 a) to the first and second bearingless motors (60, 70).

The drive shaft (20) is therefore capable of rotating the impeller (3 a)of the turbo compressor (1).

—Compression Mechanism—

The compression mechanism (3) is configured to compress a fluid (arefrigerant in this example) and has the impeller (3 a) as a majorelement. The impeller (3 a) has a plurality of blades, and thus hassubstantially a conical outer shape. The impeller (3 a) is accommodatedin the impeller chamber (S1) while being connected and fixed to one endof the drive shaft (20). An intake pipe (4) and a discharge pipe (5) areconnected to the impeller chamber (S1), and a compression space (S2) isformed in an outer circumferential portion of the impeller chamber (S1).The intake pipe (4) is intended to introduce the refrigerant from theoutside into the impeller chamber (S1). The discharge pipe (5) isintended to return the high-pressure refrigerant compressed in theimpeller chamber (S1) to the outside.

<Configuration of Load Operation Control Device>

The load operation control device (10) is intended to control theoperation of the impeller (3 a) of the above-described turbo compressor(1). As already mentioned, the load operation control device (10)includes, in addition to the drive shaft (20), the touchdown bearings(30, 31), the thrust magnetic bearing (40), the drive support (50)including the first bearingless motor (60) and the second bearinglessmotor (70), the controller (90), and a power source (93).

—Touchdown Bearing—

The touchdown bearings (30, 31) are provided at two positions so as tosandwich the two bearingless motors (60, 70) in the axial direction ofthe drive shaft (20). The touchdown bearing (30), which is one of thetouchdown bearings, is provided in the vicinity of one end portion (aright end portion in FIG. 2) of the drive shaft (20). The othertouchdown bearing (31) is provided in the vicinity of the other endportion of the drive shaft (20). The touchdown bearings (30, 31) areconfigured to support the drive shaft (20) when the first and secondbearingless motors (60, 70) are not energized (i.e., when the driveshaft (20) is not floating).

—Thrust Magnetic Bearing—

As illustrated in FIG. 2, the thrust magnetic bearing (40) includesfirst and second electromagnets (41, 42) and is configured to support adisc-shaped portion (hereinafter referred to as a disk portion (21))provided at the other end portion of the drive shaft (20) (i.e., the endportion opposite to the one end portion to which the impeller (3 a) isfixed) in a non-contact manner by an electromagnetic force. The thrustmagnetic bearing (40) can control the position of the supported portion(the disk portion (21)) of the drive shaft (20) in a direction in whichthe first and second electromagnets (41, 42) face each other (i.e., theaxial direction, which is the lateral direction in FIG. 2) bycontrolling the electric current flowing through the first and secondelectromagnets (41, 42).

Although not shown in FIG. 2, a plurality of gap sensors are providednear the touchdown bearings (30, 31) and in the vicinity of the thrustmagnetic bearing (40). Each gap sensor is constituted, for example, byan eddy current displacement sensor, and detects a gap between the diskportion (21) and the thrust magnetic bearing (40), and a gap between thestator (64, 74) and the rotor (61, 71) of each of the first and secondbearingless motors (60, 70). The detection results of the gap sensorsare input to the controller (90) and used for various controls.

—Drive Support—

The drive support (50) rotates the drive shaft (20) and supports theradial load of the drive shaft (20) in a non-contact manner, by theelectromagnetic force generated by the flow of a current within apredetermined current range through the drive support (50). As alreadymentioned, the drive support (50) includes the first bearingless motor(60) and the second bearingless motor (70). The first bearingless motor(60) and the second bearingless motor (70) are arranged side by sidealong the axial direction of the drive shaft (20).

—First Bearingless Motor—

The first bearingless motor (60) is disposed in the electric motorchamber (S3) toward the impeller (3 a). The first bearingless motor (60)has a set of a rotor (61) and a stator (64). The rotor (61) is fixed tothe drive shaft (20), and the stator (64) is fixed to the innercircumferential wall of the casing (2).

FIG. 3 is a diagram illustrating a transverse section of an exampleconfiguration of the first bearingless motor (60). As shown in FIG. 3,the first bearingless motor (60) is of a consequent-pole type. Thestator (64) of the first bearingless motor (60) includes a back yoke(65), a plurality of toothed portions (not shown), driving coils (66 ato 66 c) and supporting coils (67 a to 67 c) which are wound around thetoothed portions. The rotor (61) of the first bearingless motor (60)includes a core (62) and a plurality of (four in this example) permanentmagnets (63) embedded in the core (62).

The stator (64) is made of a magnetic material (e.g., laminated steelsheets). The back yoke (65) of the stator (64) is in a cylindricalshape. The driving coils (66 a to 66 c) and the supporting coils (67 ato 67 c) are wound around each toothed portion in a distributed windingmethod. Thus, a plurality of slots (not shown) are formed in the stator(64). The driving coils (66 a to 66 c) and the supporting coils (67 a to67 c) may be wound around each toothed portion in a concentrated windingmethod.

The driving coils (66 a to 66 c) are wound around the innercircumferential side of the toothed portions. The driving coils (66 a to66 c) include a U-phase driving coil (66 a) surrounded by a thick linein FIG. 3, a V-phase driving coil (66 b) surrounded by a thick brokenline, and a W-phase driving coil (66 c) surrounded by a thin line.

The supporting coils (67 a to 67 c) are wound around the outercircumferential side of the toothed portions. The supporting coils (67 ato 67 c) include a U-phase supporting coil (67 a) surrounded by a thickline in FIG. 3, a V-phase supporting coil (67 b) surrounded by a thickbroken line, and a W-phase supporting coil (67 c) surrounded by a thinline.

The core (62) of the rotor (61) is in a cylindrical shape. The core (62)is provided with a shaft hole (not shown) for inserting the drive shaft(20) in a center portion of the core (62). The core (62) is made of amagnetic material (e.g., laminated steel sheets). Four permanent magnets(63) each having a shape along the outer circumferential surface of thecore (62) are embedded in the vicinity of the outer circumferentialsurface of the core (62) at an angular pitch (AP1) of 90° in thecircumferential direction of the rotor (61). The four permanent magnets(63) are identical in shape. The outer circumferential surface side ofeach permanent magnet (63) is an N pole, and the outer circumferentialsurface side of the core (62) between the permanent magnets (63) is apseudo S pole. The outer circumferential surface side of each permanentmagnet (63) may be an S pole.

FIG. 4 illustrates magnetic flux φ1 of magnet generated by eachpermanent magnet (63) and driving magnetic flux BM1 generated to rotatethe impeller (3 a) and the drive shaft (20) in the first bearinglessmotor (60). The first bearingless motor (60) is configured to generate adriving torque T1 in FIG. 4 (i.e., a torque for rotating the drive shaft(20) in the counterclockwise direction in FIG. 4) by the interactionbetween the magnetic flux φ1 of magnet and the driving magnetic fluxBM1. In FIG. 4, a current IM1 equivalent to the current flowing throughthe driving coils (66 a to 66 c) is shown.

FIG. 5 illustrates the magnetic flux φ1 of magnet generated by eachpermanent magnet (63) and supporting magnetic flux BS1 generated tosupport the radial load of the drive shaft (20) in a non-contact mannerin the first bearingless motor (60). The first bearingless motor (60) isconfigured to generate a supporting force F1 in FIG. 5 (i.e., a forcepushing the drive shaft (20) rightward in FIG. 5) by the interactionbetween the magnetic flux φ1 of magnet and the supporting magnetic fluxBS1. In FIG. 5, a current IS1 equivalent to the current flowing throughthe supporting coils (67 a to 67 c) is shown.

As can be seen from FIG. 5, the magnetic path of the supporting magneticflux BS1 passes through the back yoke (65) and toothed portions of thestator (64), the air gap, and the core (62) of the rotor (61). Themagnetic resistance of each of the back yoke (65), the toothed portions,and the core (62) is smaller than the magnetic resistance of thepermanent magnet (63). Thus, the first bearingless motor (60) has alower magnetic resistance of the magnetic path for generating a magneticforce for supporting the radial load of the drive shaft (20), than thesecond bearingless motor (70) provided with permanent magnets (73)around substantially the entire outer circumferential surface of therotor (71) as will be described later (that is, the second bearinglessmotor (70) including a permanent magnet (73) in the magnetic path forgenerating a magnetic force for supporting the radial load of the driveshaft (20)). This configuration allows the first bearingless motor (60)to generate a greater supporting force for supporting the radial load ofthe drive shaft (20), compared to the second bearingless motor (70).

FIG. 6 illustrates the magnetic flux φ1 of magnet generated by eachpermanent magnet (63), driving magnetic flux BM1 generated to rotate theimpeller (3 a) and the drive shaft (20), and supporting magnetic fluxBS1 generated to support the radial load of the drive shaft (20) in anon-contact manner in the first bearingless motor (60). The firstbearingless motor (60) is configured to simultaneously generate adriving torque T1 and a supporting force F1 in FIG. 6 by the interactionbetween the magnetic flux φ1 of magnet, the driving magnetic flux BM1,and the supporting magnetic flux BS1. In FIG. 6, a current IM1 and acurrent IS1 which are equivalent to the current flowing through thedriving coils (66 a to 66 c) and the supporting coils (67 a to 67 c),respectively, are shown.

—Second Bearingless Motor—

The second bearingless motor (70) is disposed in the electric motorchamber (S3) farther from the impeller (3 a) as illustrated in FIG. 2.The second bearingless motor (70) has a set of a rotor (71) and a stator(74) as illustrated in FIG. 7. The rotor (71) is fixed to the driveshaft (20), and the stator (74) is fixed to the casing (2).

Although not shown because the configuration is similar to that shown inFIG. 3, the stator (74) of the second bearingless motor (70) includes aplurality of toothed portions around which driving coils and supportingcoils are wound to form a plurality of slots.

FIG. 7 is a diagram illustrating a transverse section of an exampleconfiguration of the second bearingless motor (70). As shown in FIG. 7,the second bearingless motor (70) is of an embedded magnet type whichexhibits substantially the same behavior as a surface magnet typebearingless motor. The configuration of the stator (74) of the secondbearingless motor (70) is the same as the configuration of the stator(64) of the first bearingless motor (60). The rotor (71) of the secondbearingless motor (70) includes a core (72) and a plurality of (eight inthis example) permanent magnets (73) embedded in the core (72).

The core (72) of the rotor (71) is in a cylindrical shape. The core (72)is provided with a shaft hole (not shown) for inserting the drive shaft(20) in a center portion of the core (72). The core (72) is made of amagnetic material (e.g., laminated steel sheets). Eight permanentmagnets (73) each having a shape along the outer circumferential surfaceof the core (72) are embedded in the vicinity of the outercircumferential surface of the core (72) at an angular pitch (AP2) of45° in the circumferential direction of the rotor (71) (that is, at halfan angular pitch (AP1) of 90° in the case of the first bearingless motor(60)). The eight permanent magnets (73) are identical in shape, andidentical in shape with the four permanent magnets (63) of the firstbearingless motor (60) as well. The outer circumferential surface sideof the permanent magnets (73) exhibits N poles and S poles that appearalternately in the circumferential direction of the rotor (71).

FIG. 7 illustrates magnetic flux φ2 of magnet generated by eachpermanent magnet (73), driving magnetic flux BM2 generated to rotate theimpeller (3 a) and the drive shaft (20), and supporting magnetic fluxBS2 generated to support the radial load of the drive shaft (20) in anon-contact manner in the second bearingless motor (70). The secondbearingless motor (70) is configured to simultaneously generate adriving torque T2 (i.e., a torque for rotating the drive shaft (20) inthe counterclockwise direction in FIG. 7) and a supporting force F2(i.e., a force pushing the drive shaft (20) rightward in FIG. 7), whichare shown in FIG. 7, by the interaction between the magnetic flux φ2 ofmagnet, the driving magnetic flux BM2, and the supporting magnetic fluxBS2.

As can be seen from FIG. 7, the magnetic path of the supporting magneticflux BS2 passes through the back yoke (75) and toothed portions of thestator (74), the air gap, and the permanent magnets (73) and core (72)of the rotor (71).

The number of permanent magnets (73) in the second bearingless motor(70) is larger than the number of permanent magnets (63) in the firstbearingless motor (60). Thus, the second bearingless motor (70) exhibitsa higher density of magnetic flux generated by the permanent magnets(73), as compared to the first bearingless motor (60) (see FIG. 4). Thisconfiguration allows the second bearingless motor (70) to generate agreater driving torque T2 for rotating the impeller (3 a) and the driveshaft (20), compared to the first bearingless motor (60).

—Controller—

The controller (90) is comprised of a microcomputer (91) and a memory(92) storing software or the like for operating the microcomputer (91).The controller (90) generates and outputs a voltage command value (athrust voltage command value) for controlling a voltage to be suppliedto the thrust magnetic bearing (40), and a voltage command value (amotor voltage command value) for controlling a voltage to be supplied tothe first and second bearingless motors (60, 70) so that the drive shaft(20) is positioned at a desired position.

The voltage command values are generated using, for example, a detectionvalue of a gap sensor (not shown) capable of detecting a gap between thedisk portion (21) and the thrust magnetic bearing (40), a detectionvalue of a gap sensor (not shown) capable of detecting a gap between thestator (64, 74) and the rotor (61, 71) in the first and secondbearingless motors (60, 70), and information on target rotational speedsof the impeller (3 a) and the drive shaft (20).

In particular, the microcomputer (91) of the controller (90) accordingto the first embodiment functions as an operation control section (91 a)(which corresponds to the control section). The operation controlsection (91 a) calculates a degree of margin of the total magnetic fluxof the first and second bearingless motors (60, 70) (hereinafterreferred to as a magnetic flux margin degree), and controls theoperating condition of the turbo compressor (1) (specifically, theimpeller (3 a) of the compression mechanism (3)) which is a load of thefirst and second bearingless motors (60, 70), based on the calculatedmagnetic flux margin degree. This operation control may be referred toas extension control for the operation region of the turbo compressor(1), and will be described in detail later.

The microcomputer (91) of the controller (90) according to the firstembodiment also functions as an update section (91 b). The memory (92)stores a predetermined operation region (which will be described later)comprised of a plurality of regions. The update section (91 b)overwrites the memory (92) when the predetermined operation region isupdated.

—Power Source—

The power source (93) supplies voltages to the thrust magnetic bearing(40) and the first and second bearingless motors (60, 70) based on thethrust voltage command value and the motor voltage command value fromthe controller (90), respectively. For example, the power source (93)may be configured as a pulse width modulation (PWM) amplifier.

<Operation Region of Turbo Compressor>

An operation region of the turbo compressor (1) will be described withreference to FIG. 8. In FIG. 8, the horizontal axis represents a volumeflow rate of the refrigerant, and the vertical axis represents the head.The turbo compressor (1) can be operated in a predetermined operationregion by the flow of a current in a predetermined current range throughthe drive support (50) (i.e., the first and second bearingless motors(60, 70) in the first embodiment) by the power source (93).

The predetermined operation region mainly includes a steady stateoperation region (A), a high-load torque region (B), and a turbulenceregion (C) which are inside a surge line indicated by a heavy dot-dashline in FIG. 8, and a surging region (D) outside the surge line.

The steady state operation region (A) is indicated by the referencenumeral A in FIG. 8, in which region the load torque of the impeller (3a) and the drive shaft (20) (i.e., the driving torque T1 and T2 fordriving the impeller (3 a) and the drive shaft (20)) is relatively low,and the radial load of the drive shaft (20) is relatively low as well.

The high-load torque region (B) is indicated by the reference numeral Bin FIG. 8, in which region the load torque of the impeller (3 a) and thedrive shaft (20) is relatively high, and the radial load of the driveshaft (20) is relatively high as well.

The turbulence region (C) is indicated by the reference numeral C inFIG. 8, in which region the load torque of the impeller (3 a) and thedrive shaft (20) is relatively low, and the radial load of the driveshaft (20) is relatively high.

The surging region (D) is indicated by the reference numeral D in FIG.8, in which region the load torque of the impeller (3 a) and the driveshaft (20) is relatively low, and the radial load of the drive shaft(20) is relatively high. The radial load of the drive shaft (20) in theturbo compressor (1) is maximized at a predetermined point in thesurging region (D). When the turbo compressor (1) is operated at thispredetermined point, a value of the supporting magnetic flux BS ismaximized, and a maximum supporting force current flows to thesupporting coils (67 a to 67 c) of each bearingless motor (60, 70).

In the following description, a case in which the turbo compressor (1)is operated in the steady state operation region (A) and the high-loadtorque region (B) is referred to as a “normal operation,” and the steadystate operation region (A) and the high-load torque region (B) arecollectively referred to as a “first operable region.” In the presentembodiment, the “first operable region” is a default region that is setin advance. The turbulence region (C) is also referred to as a “regionwhere rotating stall occurs.”

<Calculation of Margin Degree of Total Magnetic Flux>

How the operation control section (91 a) calculates the magnetic fluxmargin degree will be described in detail.

The operation control section (91 a) obtains a total amount of themagnetic flux generated in each of the bearingless motors (60, 70). Theoperation control section (91 a) subtracts the obtained total amount ofthe magnetic flux from a predetermined limit of the total magnetic fluxof each bearingless motor (60, 70), and thereby obtains the magneticflux margin degree represented by the thus obtained difference (theresult of the subtraction).

As already mentioned, the magnetic flux generated in the respectivefirst and second bearingless motors (60, 70) includes, for example: thedriving magnetic flux BM1 and BM2 generated in the first and secondbearingless motors (60, 70), respectively, for rotating the impeller (3a) and the drive shaft (20); the supporting magnetic flux BS1 and BS2generated in the first and second bearingless motors (60, 70),respectively, for supporting the radial load of the drive shaft (20) ina non-contact manner; and the magnetic flux φ1 and φ2 generated by thepermanent magnets (63, 73), in the predetermined operation region of theturbo compressor (1) shown in FIG. 8. First, the operation controlsection (91 a) calculates, for each of the bearingless motors (60, 70),the amount of magnetic flux at a slot (not shown) where the total valueof the driving magnetic flux BM1 and BM2, the supporting magnetic fluxBS1 and BS2, and the magnetic flux φ1 and φ2 of magnet is the largestamong all of the slots (not shown) formed in the stators (64, 74).

Specifically, assuming that the amount of the driving magnetic flux BM1and BM2 is “ΦM,” that the amount of the supporting magnetic flux BS1 andBS2 is “ΦS,” and that the amount of the magnetic flux φ1 and φ2 ofmagnet is “ΦP,” the magnetic flux amount Φn of the n^(th) slot at acertain moment can be expressed as follows.[Equation 1]Φ_(n)=Φ_(Mn)+Φ_(Sn)+Φ_(Pn)=Φ_(Mn)(i _(M),θ_(M),θ_(R))+Φ_(sn)(i_(S),θ_(S),θ_(R))+Φ_(pn) n(θ_(R))  (1)

In the above equation, each argument is an instantaneous value. In theabove equation, the “iM” represents a driving equivalent current (acurrent equivalent to the current flowing through the driving coils),and is a parameter which contributes to the strength of the entiredriving magnetic flux BM1 and BM2. The “iS” represents a supportingequivalent current (a current equivalent to the current flowing throughthe supporting coils), and is a parameter which contributes to thestrength of the entire supporting magnetic flux BS1 and BS2. The “θM”represents an electrical angle of the driving magnetic flux BM1 and BM2,and is a parameter which contributes to the magnetic resistance at eachslot for the driving magnetic flux BM1 and BM2 with respect to eachslot. The “θS” represents an electrical angle of the supporting magneticflux BS1 and BS2, and is a parameter which contributes to the magneticresistance at each slot for the supporting magnetic flux BS1 and BS2with respect to each slot. The “θR” represents an electrical angle ofthe rotor, and is a parameter which contributes to the magneticresistance.

The magnetic flux amount Φn of the n^(th) slot at a certain instant isobtained by the expansion of the above equation (1) as shown below.

$\begin{matrix}\left\lbrack {{Equation}\mspace{14mu} 2} \right\rbrack & \; \\{\Phi_{n} = {\frac{N_{M}i_{M}}{R_{Mn}\left( {\theta_{M},\theta_{R}} \right)} + \frac{N_{S}i_{S}}{R_{Sn}\left( {\theta_{S},\theta_{R}} \right)} + \frac{F_{p}}{R_{p_{n}}\left( \theta_{R} \right)}}} & (2)\end{matrix}$

In the above equation, the “NM” represents the number of windings of thedriving coils (66 a to 66 c) in each bearingless motor (60, 70). The“NS” represents the number of windings of the supporting coils (67 a to67 c) in each bearingless motor (60, 70). The “RMn” represents themagnetic resistance at each slot for the driving magnetic flux BM1 andBM2 at the n^(th) slot in each bearingless motor (60, 70). The “RSn”represents the magnetic resistance at each slot for the supportingmagnetic flux BS1 and BS2 at the n^(th) slot in each bearingless motor(60, 70). The “RPn” represents the magnetic resistance of the permanentmagnets (63, 73) at the n^(th) slot in each bearingless motor (60, 70).The “FP” represents a magnetomotive force of the permanent magnets (63,73) in each bearingless motor (60, 70).

Thus, the maximum total magnetic flux amount ΦMax (which corresponds toa total magnetic flux amount of the magnetic flux generated at the drivesupport (50)) at the slots of each bearingless motor (60, 70) can beexpressed as follows.

$\begin{matrix}{\mspace{79mu}\left\lbrack {{Equation}\mspace{14mu} 3} \right\rbrack} & \; \\{\Phi_{Max} = {{\max\limits_{n}\left\{ \Phi_{n} \right\}} = {\max\limits_{n}\left\{ {\frac{N_{M}i_{M}}{R_{Mn}\left( {\theta_{M},\theta_{R}} \right)} + \frac{N_{S}i_{S}}{R_{Sn}\left( {\theta_{S},\theta_{R}} \right)} + \frac{F_{p}}{R_{p_{n}}\left( \theta_{R} \right)}} \right\}}}} & (3)\end{matrix}$

Assuming that a predetermined limit of the total magnetic flux amount ofeach bearingless motor (60, 70) is “ΦULim,” the magnetic flux margindegree MΦ in each bearingless motor (60, 70) can be expressed asfollows.

[Equation 4]M _(Φ)=Φ_(ULim)−Φ_(Max)  (4)

Thus, the magnetic flux margin degree MΦ can be expressed as followsfrom the equations (3) and (4).

$\begin{matrix}\left\lbrack {{Equation}\mspace{14mu} 5} \right\rbrack & \; \\{M_{\Phi} = {\Phi_{ULim} - {\max\limits_{n}\left\{ {\frac{N_{M}i_{M}}{R_{Mn}\left( {\theta_{M},\theta_{R}} \right)} + \frac{N_{S}i_{S}}{R_{Sn}\left( {\theta_{S},\theta_{R}} \right)} + \frac{F_{p}}{R_{p_{n}}\left( \theta_{R} \right)}} \right\}}}} & (5)\end{matrix}$

The limit ΦULim of the total magnetic flux amount is, for example, avalue determined by, and unique to, the material characteristics of thebearingless motors (60, 70).

In the following description, the sum of the magnetic flux margindegrees MΦ of the bearingless motors (60, 70) obtained by the aboveequation (5) is used to control operation of the compression mechanism(3), as an example.

<Control Operation of Bearingless Motor Based on Magnetic Flux MarginDegree>

—Extension Control for Operation Region—

FIG. 9 is a graph for explaining extension control for the operationregion. In FIG. 9, the horizontal axis represents an output of the airconditioner (100), and the vertical axis represents a temperature of theaqueous medium flowing into the condenser (120) in the outdoor-sidewater circuit (150). The “OUTPUT OF AIR CONDITIONER” on the horizontalaxis in FIG. 9 is a parameter correlating with the “VOLUME FLOW RATE OFREFRIGERANT” on the horizontal axis in FIG. 8. The output of the airconditioner (100) represents the amount of heat per unit time which istaken away from the aqueous medium by the evaporator (140) of the airconditioner (100) shown in FIG. 1 (i.e., temperature condition of theaqueous medium). The “TEMPERATURE OF AQUEOUS MEDIUM FLOWING INCONDENSER” on the vertical axis in FIG. 9 is a parameter correlatingwith the “HEAD” on the vertical axis in FIG. 8.

In FIG. 9, the area enclosed by the broken line, the vertical axis, andthe horizontal axis corresponds to the predetermined “first operableregion” including the normal operation region (A) and the high-loadtorque region (B) in FIG. 8. In FIG. 9, the area sandwiched between thesurge line indicated by the dot-dash line and the boundary line of thefirst operable region indicated by the broken line corresponds to the“region where rotating stall occurs,” which is the turbulence region (C)in FIG. 8. In FIG. 9, the region above the surge line indicated by thedot-dash line corresponds to the surging region (D) in FIG. 8.

The surging will be described below. FIG. 10 is a graph for explaining amechanism of surging. The turbo compressor (1) (specifically, theimpeller (3 a)) is designed such that the smaller the volume flow rateof the refrigerant flowing into the turbo compressor (1) is, the higherthe head becomes, in a state in which the rotational speed is constant.In the predetermined first operable region of FIG. 10, the headdecreases when the volume flow rate of the refrigerant increases due toa disturbance. The reduction in head means a reduction in dischargepressure. In contrast, the head increases (i.e., the discharge pressureincreases) when the volume flow rate of the refrigerant is reduced dueto a disturbance, which allows the volume flow rate of the refrigerantto be relatively stable.

However, if the volume flow rate of the refrigerant is further reducedwhile the rotational speed of the turbo compressor (1) (specifically,the impeller (3 a)) is constant, the angle of blades of the impeller (3a) with respect to the refrigerant flow (i.e., the angle of attack) istoo large, so that the stall phenomenon occurs in some of the blades.This phenomenon occurs in a rotating manner so as to propagate among theblades of the impeller (3 a), and is thus called “rotating stall” (theturbulence region (C) in FIG. 10). During the rotating stall, thepressure distribution near the impeller (3 a) is non-uniform, and apulsating exciting force is applied to the impeller (3 a).

Further, if the volume flow rate of the refrigerant is reduced to anextremely small value while the rotational speed is constant, the volumeflow rate of the refrigerant described above becomes unstable becausethe head converges to substantially a constant value, that is, thegradient of the head to the volume flow rate of the refrigerantapproaches zero (0) (the surging region (D) in FIG. 10). The volume flowrate of the refrigerant in the entire flow path from the evaporator(140) to the condenser (120) in the refrigerant circuit (110) thereforebecomes very unstable, which results in transmitting a larger pulsatingexciting force to the impeller (3 a). This phenomenon is called“surging.” The exciting force causes the turbo compressor (1) tovibrate, making the operation of the turbo compressor (1) unstable. Theexciting force is a cause of an excessive load applied to mechanicalcomponents constituting the turbo compressor (1), and may damage themechanical components in the worst case.

To avoid such surging, in general, the predetermined first operableregion is set to be a region inside the surge line except the turbulenceregion (C) (specifically, the steady state operation region (A) and thehigh-load torque region (B)) as already described with reference to FIG.9.

The surging may occur when, for example, the power supply to the airconditioner (100) from a commercial power source (not shown) is suddenlyinterrupted by a power failure while the turbo compressor (1) isoperated near the boundary line of the predetermined first operableregion. When the supply power to the air conditioner (100) is cut off,the operation of the turbo compressor (1) is also stopped. If thishappens, the volume flow rate of the refrigerant suddenly decreaseswithout a significant change in the head of the turbo compressor (1),and the head of the turbo compressor (1) also decreases thereafter. Thisis because the operating state of the turbo compressor (1) maytransition, even temporarily, from the predetermined first operableregion to the surging region (D) beyond the surge line, in a period fromthe sudden decrease in the volume flow rate of the refrigerant to thedecrease in the head of the turbo compressor (1).

To address this phenomenon, when the operation control section (91 a)according to the first embodiment determines that the total magneticflux amount of the first and second bearingless motors (60, 70) stillhas a margin with respect to the limit of the total magnetic fluxamount, based on the magnitude of the magnetic flux margin degrees ofthe first and second bearingless motors (60, 70), the operation controlsection (91 a) controls the operating condition of the turbo compressor(1), which is a load, such that the turbo compressor (1) is operated inthe turbulence region (C). That is, the operation control section (91 a)extends the region where the operation of the turbo compressor (1) ispermitted, from the predetermined first operable region (the regionbelow the broken line in FIG. 9) to a “second operable region” which isa region having the first operable region plus an “extended operationregion” that is hatched in FIG. 9.

The extension of the operation region means that the turbo compressor(1) is operated at a point closer to the surge line than a point in thepredetermined first operable region. This configuration may increase thepossibility that the operating state of the turbo compressor (1)temporarily transitions to the surging region (D) beyond the surge line.However, the operation control section (91 a) according to the firstembodiment performs a control on the turbo compressor (1) so that theturbo compressor (1) can well withstand the rotating stall and thesurging, in addition to the extension of the operation region.

Specifically, the operation control section (91 a) performs a control sothat the margin of the total magnetic flux amount of the first andsecond bearingless motors (60, 70) is used to generate a supportingforce for supporting the drive shaft (20), based on the magnetic fluxmargin degree of the first and second bearingless motors (60, 70). Asalready mentioned, each bearingless motor (60, 70) is capable ofgenerating the driving magnetic flux BM1, BM2 and the supportingmagnetic flux BS1, BS2. The operation control section (91 a) generatesand outputs the voltage command value (i.e., the motor voltage commandvalue) so that the margin of the total magnetic flux amount of the firstand second bearingless motors (60, 70) is used not to generate thedriving magnetic flux BM1, BM2, but to generate the supporting magneticflux BS1, BS2.

Specifically, in operating the turbo compressor (1) in the turbulenceregion (C), the operation control section (91 a) transmits the motorvoltage command value to the power source (93) so that the ratio of thecurrent IS for generating the supporting magnetic flux BS to the currentIM (i.e., the sum of the current flowing through the supporting coils(67 a to 67 c) of the first and second bearingless motors (60, 70)) forgenerating the driving magnetic flux BM (i.e., the sum (BM1+BM2) of thedriving magnetic fluxes generated at the first and second bearinglessmotors (60, 70)) is increased more than in the normal operation, whencompared at the same rotational speed. During this operation, the powersource (93) supplies a voltage to the first and second bearinglessmotors (60, 70), based on the motor voltage command value transmittedfrom the operation control section (91 a), so that the ratio of thecurrent IS flowing to the supporting coils (67 a to 67 c) to the currentIM flowing to the driving coils (66 a to 66 c) in the first and secondbearingless motors (60, 70) is increased.

As a result, in the turbulence region (C) (i.e., a rotating stallregion), a supporting force for supporting the drive shaft (20), whichsupporting force is capable of withstanding the exciting force caused bythe rotating stall (and surging), is generated at the first and secondbearingless motors (60, 70). Damage of the mechanical componentsconstituting the turbo compressor (1) caused by the rotating stall andthe surging can thus be reduced. Such extension control for theoperation region allows using the turbo compressor (1) in the operationregion (the extended operation region in FIG. 9) which has beenintentionally refrained from use to avoid the occurrence of the rotatingstall or surging. The range of situations in which the turbo compressor(1) is used is thus widened.

—Flow of Extension Control for Operation Region—

Flow of extension control for operation region will be described belowwith reference to FIG. 11.

First, the operation control section (91 a) determines whether theextension control for the operation region is permitted or not (stepSt11). Whether the extension control for the operation region ispermitted or not can be appropriately determined by an installer whoinstalls the air conditioner (100) or a user, for example.

If the expansion control for the operation region is not permitted (Noin step St11), the operation control section (91 a) sets the output ofthe air conditioner (100) and the temperature of the aqueous mediumflowing into the condenser (120) to values for operation of the turbocompressor (1) in the first operable region (step St12). In other words,in this case, the operation region is not extended, and the turbocompressor (1) is operated within the predetermined first operableregion shown in FIG. 9 and FIG. 10.

If the extension control for the operation range is permitted (Yes instep St11), the operation control section (91 a) estimates the totalmagnetic flux amount in the first and second bearingless motors (60, 70)in the current state by calculation based on the above equation (3)(step St13). The operation control section (91 a) then calculates themargin degree of total magnetic flux of the first and second bearinglessmotors (60, 70) based on the above equation (5) (step St14). Theoperation control section (91 a) compares the obtained margin degree oftotal magnetic flux with a predetermined value (step St15).

If the obtained margin degree of total magnetic flux is greater than orequal to the predetermined value (Yes in step St15), the operationcontrol section (91 a) performs a control on at least one of thecomponents of the turbo compressor (1) and the refrigerant circuit (110)so as to increase the temperature (discharge temperature) of therefrigerant discharged from the turbo compressor (1) so that thetemperature of the aqueous medium flowing into the condenser (120) israised from the current water temperature, while keeping the output ofthe air conditioner (100) constant (St16). The state in which theobtained margin degree of total magnetic flux is greater than or equalto the predetermined value means that the first and second bearinglessmotors (60, 70) have a margin for the magnetic flux to be generatedtherein. In a situation of cooling the interior of a room, thetemperature of water flowing into the condenser (120) rises as theoutdoor temperature rises, which increases the refrigerant temperaturein the condenser (120) and the refrigerant pressure accordingly. In thissituation as well, the operation control section (91 a) controls theturbo compressor (1) to adjust at least one of the rotational speed ofthe turbo compressor (1) and the flow rate of the refrigerant in therefrigerant circuit (110) so as to increase the discharge pressure ofthe turbo compressor (1) and raise the discharge temperature of therefrigerant, in a case in which the aqueous medium on the indoor side isconstantly cooled to a certain temperature, regardless of the outdoortemperature (i.e., in a case in which the output of the air conditioner(100) is constant). For example, the operation control section (91 a)controls the turbo compressor (1) to increase the rotational speed ofthe turbo compressor (1) and/or reduce the flow rate of the refrigerantso as to increase the discharge pressure of the turbo compressor (1) andraise the discharge temperature of the refrigerant.

The increase in the discharge pressure of the turbo compressor (1) isequivalent to the rise of the head of the turbo compressor (1). That is,step St16 in FIG. 11 means that the operation region of the turbocompressor (1) is extended from the predetermined first operable regionshown in FIG. 9 to the second operable region including the firstoperable region plus the extended operation region. Step St16 in FIG. 11further means that the operation limit point of the turbo compressor (1)has transitioned from a point (triangular mark in FIG. 9) near theboundary line of the predetermined first operable region to an operatingpoint (round mark in FIG. 9) as a result of a change toward the regionwhere the amount of use of the magnetic flux is increased. In step St16,the margin of the magnetic flux associated with the extension of theoperation region is used to generate the supporting magnetic flux BS1and BS2 of the first and second bearingless motors (60, 70), therebyincreasing the drive supporting force of the drive shaft (20) and theimpeller (3 a) included in the compression mechanism (3).

After step St16, the update section (91 b) resets the predeterminedoperation region currently stored in the memory (92) to thepredetermined extended operation region which has been extended in stepSt16 (step St17). That is, the predetermined operation region includingthe second operable region, which is a region after extension, is usedas a default value in the next extension control for the operationregion.

If the obtained margin degree of total magnetic flux is below thepredetermined value (No in step St15), the operation control section (91a) performs a control on at least one of the components of the turbocompressor (1) and the refrigerant circuit (110) so as to reduce thetemperature (discharge temperature) of the refrigerant discharged fromthe turbo compressor (1) so that the temperature of the aqueous mediumflowing into the condenser (120) drops from the current watertemperature, while keeping the output of the air conditioner (100)constant (St18). The state in which the obtained margin degree of totalmagnetic flux is below the predetermined value means that the first andsecond bearingless motors (60, 70) do not have a margin for the magneticflux to be generated therein. Thus, the operation control section (91 a)controls the turbo compressor (1) to adjust at least one of therotational speed of the turbo compressor (1) and the flow rate of therefrigerant in the refrigerant circuit (110) so as to reduce thedischarge pressure of the turbo compressor (1) and drop the dischargetemperature of the refrigerant. For example, the operation controlsection (91 a) controls the turbo compressor (1) to reduce therotational speed of the turbo compressor (1) and/or increase the flowrate of the refrigerant so as to reduce the temperature of therefrigerant discharged from the turbo compressor (1). In this case, theoperation region of the turbo compressor (1) is not extended because thehead is reduced.

<Advantages>

In the first embodiment, it is possible to extend the operation regionof the turbo compressor (1) to the maximum controllable extent, bychanging the operating condition of the turbo compressor (1) inaccordance with the magnetic flux margin degree of the drive support(50). Specifically, the operation control section (91 a) performs acontrol or the like in which the margin of the magnetic flux is used togenerate the supporting magnetic flux in accordance with the magneticflux margin degree of the drive support (50) in the region where therotating stall occurs. The turbo compressor (1) is therefore operable,without any problem, not only in the first operable region shown in FIG.9, but also in the region where the rotating stall occurs (theturbulence region (C), that is, the extended operation region), forexample. The turbo compressor (1) is therefore operable in a widervariety of operating state.

In particular, the drive support (50) has the first bearingless motor(60) and the second bearingless motor (70). These bearingless motors(60, 70) are capable of changing the ratio between the supportingmagnetic flux and the driving magnetic flux in accordance with theoperating state of the load and the magnetic flux margin degree. Thatis, the control (such as decreasing the driving magnetic flux andincreasing the supporting magnetic flux, which are generated at thebearingless motors (60, 70)) can be performed, while ensuring a certainmagnetic flux margin degree, so that the turbo compressor (1) canwithstand the surging phenomenon in the case in which the operationregion of the turbo compressor (1) is extended. The turbo compressor (1)is therefore operable in a wider variety of operating state without aproblem.

Further, the operation control section (91 a) calculates, as a totalmagnetic flux amount, the amount of magnetic flux at a slot where thetotal value of the driving magnetic flux BM1 and BM2, the supportingmagnetic flux BS1 and BS2, and the magnetic flux φ1 and φ2 of thepermanent magnets (63, 73) included in the rotors (61, 71) is thelargest among the plurality of slots formed in the stators (64, 74). Itis therefore possible to obtain the accurate total magnetic flux amountgenerated in the bearingless motors (60, 70). As a result, magneticsaturation is avoided, which makes it possible to extend the operationregion as much as possible while maintaining the accuracy in control ofthe drive support (50).

If the magnetic flux margin degree exceeds the predetermined value as instep St16 in FIG. 11, it is possible to determine that the drive support(50) has a margin in terms of magnetic flux. The operation controlsection (91 a) therefore increases the head (compression work) of theturbo compressor (1) (i.e., increases the temperature of the refrigerantdischarged from the turbo compressor (1)), thereby raising thetemperature of the aqueous medium flowing into the condenser (120). Theincrease in the temperature of the aqueous medium flowing into thecondenser (120) means that the refrigerant circuit (110) is capable ofperforming the refrigeration cycle even in, for example, ahigh-temperature outdoor environment, which means that the operationregion of the load is extended.

On the other hand, if the magnetic flux margin degree is below thepredetermined value as in step St18 in FIG. 11, it is possible todetermine that the drive support (50) does not have a margin in terms ofmagnetic flux. The operation control section (91 a) therefore decreasesthe temperature of the refrigerant discharged from the turbo compressor(1) thereby decreasing the head (compression work) of the turbocompressor (1). It is therefore possible to avoid the occurrence ofsurging and rotating stall in the turbo compressor (1).

As shown in step St17 in FIG. 11, the update section (91 b) updates thepredetermined operation region, based on the operating state of theturbo compressor (1) at the time when the control section (91 a) raisesthe temperature of the refrigerant discharged from the turbo compressor(1). This configuration allows the next operation of the turbocompressor (1) to be performed with reference to the extended operationregion.

<<Second Embodiment>>

In the first embodiment, as shown in steps St16 and St18 in FIG. 11, theoutput of the air conditioner (100) is maintained at a constant value inthe control for dropping the temperature (discharge temperature) of therefrigerant based on the magnetic flux margin degree. In the secondembodiment, unlike the first embodiment, the output of the airconditioner (100) is changed in the control for dropping the temperature(discharge temperature) of the refrigerant based on the magnetic fluxmargin degree.

The second embodiment is different from the first embodiment only inthat part of the flow of the extension control for the operation regionshown in FIG. 12 is different from that in FIG. 11 according to thefirst embodiment. The configurations of the turbo compressor (1), theair conditioner (100), and the load operation control device (10) arethe same as those of the first embodiment. Only the portions in FIG. 12which are different from FIG. 11 will be described in the followingdescription.

—Flow of Extension Control for Operation Region—

Steps St11 to St15 in FIG. 12 are the same as those in FIG. 11.

In step St15 in FIG. 12, if the obtained margin degree of total magneticflux is greater than or equal to the predetermined value (Yes in stepSt15), the operation control section (91 a) adjusts at least one of therotational speed of the turbo compressor (1) and the flow rate of therefrigerant flowing through the refrigerant circuit (110) so as todecrease the output of the air conditioner (100), while keeping thetemperature of the aqueous medium flowing in the condenser (120)constant (St26).

After step St26, the update section (91 b) resets the predeterminedoperation region currently stored in the memory (92) to thepredetermined extended operation region which has been extended in stepSt26 (step St27). That is, the predetermined operation region includingthe second operable region, which is a region after extension, is usedas a default value in the next extension control for the operationregion.

If the margin degree of total magnetic flux is below the predeterminedvalue (No in step St15), the operation control section (91 a) adjusts atleast one of the rotational speed of the turbo compressor (1) and theflow rate of the refrigerant flowing through the refrigerant circuit(110) so as to increase the output of the air conditioner (100), whilekeeping the temperature of the aqueous medium flowing in the condenser(120) constant (St28).

<Advantages>

With reference to FIG. 9, the lower the output of the air conditioner(100) is, the more likely it is that the turbo compressor (1) enters theturbulence region (C). In contrast, the higher the output of the airconditioner (100) is, the less likely it is that the turbo compressor(1) enters the turbulence area (C).

If the magnetic flux margin degree exceeds the predetermined value andthe drive support (50) has a margin in terms of magnetic flux as in stepSt26, it is possible to use the margin for the magnetic flux forgeneration of the supporting magnetic flux BS1 and BS2. Thus, in thesecond embodiment, the output of the air conditioner (100) isintentionally reduced to cause the operating state of the turbocompressor (1) to transition to the turbulence region (C). This meansthat the operation region of the load is extended.

On the other hand, if the magnetic flux margin degree is below thepredetermined value and the drive support (50) does not have a margin interms of magnetic flux, it means that the drive support (50) does nothave enough magnetic flux that can be used for the generation of thesupporting magnetic flux BS1 and BS2. Thus, in the second embodiment,the output of the air conditioner (100) is increased so that theoperating state of the turbo compressor (1) is less likely to transitionto the turbulence region (C). It is therefore possible to avoid theoccurrence of surging and rotating stall in the turbo compressor (1).

<<Other Embodiments>>

The load operation control device (10) is also applicable to a drivesupport (50) which includes, in place of the two bearingless motors (60,70), a radial magnetic bearing which generates a drive supporting forcefor supporting the drive shaft, and a dynamo-electric machine which isother than the bearingless motor and generates a rotational drivingforce for rotating the drive shaft.

Further, the load operation control device (10) is also applicable to adrive support (50) which includes one radial magnetic bearing and onebearingless motor.

In a case of the drive support (50) comprised of a plurality ofbearingless motors, the number of the bearingless motors is not limitedto two, and may be one or three or more.

The type of the bearingless motors (60, 70) is not limited to theconsequent-pole type or the like.

The bearingless motors (60, 70) may be configured to have a coil havingboth driving and supporting functions, instead of separate coilsindependently having driving and supporting functions.

The rotor (61, 71) and the stator (64, 74) may be made of a materialother than laminated steel sheets.

The number of impeller (3 a) of the turbo compressor (1) is not limitedto one, but may be two or more. For example, one impeller may beattached to each end of the drive shaft (20).

The load of the load operation control device (10) may be anything thatmay experience surging. The load is not limited to the turbo compressor(1), and may be a pump or the like.

In the case where the bearingless motor does not have a permanentmagnet, the total magnetic flux amount generated in the bearinglessmotors (60, 70) is determined by the total value of the driving magneticflux φM and the supporting magnetic flux φS without adding the magneticflux φP of magnet.

The method for calculating the magnetic flux margin degree using theequations (1) to (5) is an example. The magnetic flux margin degree maybe calculated by a method different from the method using the equations(1) to (5). For example, a peak value of the magnetic flux margin degreeMΦ per predetermined time and/or a lowpass filtered value of themagnetic flux margin degree MΦ may be used as the magnetic flux margindegree MΦ.

The first and second embodiments illustrate the air conditioner (100) asa chiller unit, but the air conditioner (100) is not limited to achiller unit.

The predetermined operation region is updated in step St17 in FIG. 11and step St27 in FIG. 12, but these steps St17 and St27 are notessential.

Steps St16 and St18 in FIG. 11 illustrate a case in which thetemperature of the aqueous medium flowing into the condenser (120) ischanged from the current water temperature, while keeping the output ofthe air conditioner (100) constant. However, the temperature of theaqueous medium flowing into the evaporator (140), instead of thecondenser (120), may be changed from the current water temperature.Specifically, in step St16, the operation control section (91 a) maydecrease the temperature of the aqueous medium flowing into theevaporator (140) from the current water temperature, while keeping theoutput of the air conditioner (100) constant. In step St18, theoperation control section (91 a) may increase the temperature of theaqueous medium flowing into the evaporator (140) from the current watertemperature, while keeping the output of the air conditioner (100)constant.

INDUSTRIAL APPLICABILITY

As can be seen from the foregoing description, the present invention isuseful as a system for controlling operation of a load that mayexperience surging in a configuration of a device having a drive shaftwhich drives the load and is rotated and supported in a non-contactmanner by a drive support.

DESCRIPTION OF REFERENCE CHARACTERS

-   1 Turbo Compressor-   10 Load Operation Control Device (Load Operation Control System)-   20 Drive Shaft-   50 Drive Support-   60 First Bearingless Motor-   61 Rotor-   64 Stator-   70 Second Bearingless Motor-   71 Rotor-   74 Stator-   91 a Operation Control Section (Control Section)-   91 b Update Section

The invention claimed is:
 1. A load operation control system,comprising: a drive shaft which rotates a load; a drive support whichrotates the drive shaft and supports a radial load of the drive shaft ina non-contact manner, by an electromagnetic force generated by flow of acurrent within a predetermined current range through the drive support;and a control section which controls an operating condition of the loadbased on a magnetic flux margin degree expressed by a differencebetween: a total magnetic flux amount including driving magnetic fluxand supporting magnetic flux; and a predetermined limit of the totalmagnetic flux amount for the drive support, the driving magnetic fluxbeing generated at the drive support for rotating the drive shaft andthe supporting magnetic flux being generated at the drive support forsupporting the radial load of the drive shaft in a predeterminedoperation region of the load.
 2. The system of claim 1, wherein thedrive support has at least one bearingless motor having a set of a rotorand a stator to rotate the drive shaft and supporting the radial load ofthe drive shaft in a non-contact manner.
 3. The system of claim 2,wherein the control section calculates, as the total magnetic fluxamount, an amount of magnetic flux at a slot where a total value of thedriving magnetic flux and the supporting magnetic flux is the largestamong a plurality of slots formed in the stator.
 4. The system of claim3, wherein the control section calculates the total magnetic fluxamount, using a sum of the driving magnetic flux, the supportingmagnetic flux, and further magnetic flux of a permanent magnet includedin the rotor as the total value.
 5. The system of claim 1, wherein theload is a turbo compressor which compresses a refrigerant in arefrigerant circuit configured to perform a refrigeration cycle, and thecontrol section if the magnetic flux margin degree exceeds apredetermined value, adjusts at least one of a rotational speed of theturbo compressor and a flow rate of the refrigerant such that atemperature of the refrigerant discharged from the turbo compressorincreases, and if the magnetic flux margin degree is below thepredetermined value, adjusts at least one of the rotational speed of theturbo compressor and the flow rate of the refrigerant such that thetemperature of the refrigerant discharged from the turbo compressordecreases.
 6. The system of claim 5, further comprising: an updatesection which updates the predetermined operation region, based on anoperating state of the turbo compressor at a time when the controlsection increases the temperature of the refrigerant discharged from theturbo compressor.
 7. The system of claim 1, wherein the load is a turbocompressor which compresses a refrigerant in a refrigerant circuitconfigured to perform a refrigeration cycle, and the control section ifthe magnetic flux margin degree exceeds a predetermined value, adjustsat least one of a rotational speed of the turbo compressor and a flowrate of the refrigerant such that an output of an air conditioner havingthe refrigerant circuit decreases, and if the magnetic flux margindegree is below the predetermined value, adjusts at least one of therotational speed of the turbo compressor and the flow rate of therefrigerant such that the output of the air conditioner increases. 8.The system of claim 7, further comprising: an update section whichupdates the predetermined operation region, based on an operating stateof the turbo compressor at a time when the control section decreases theoutput of the air conditioner.